Apparatus for preparing a dental filling

ABSTRACT

Pre-packaged dental filling ingredients for use by dentists. The ingredients which are in part liquid and in part powder are encapsulated and sealed tightly in a flexible-membrane formed bag and therein separated one from the other, which separation is released by the compression of the bag to cause the ingredients to be successively brought into contact and mixed together. The mixture, confined within the bag, is spatulated to form a paste or semi-solid, ready for application to patient&#39;&#39;s tooth. The spatulation may be carried out advantageously with apparatus adapted to compressively roll over the flexible bag supported on a surface or squeeze on the bag against the surface.

United States Patent lnoue et al.

APPARATUS FOR PREPARING A DENTAL FILLING Inventors: Kiyoshi Inoue, Tokyo; Akihiko Shimizu, Sagamihara, both of Japan Assignee: Inoue-Japax Research Incorporated,

Yokohama-shi, Japan Filed: Dec. 15, 1972 Appl. No.: 315,353

Related US. Application Data Division of Ser. No. 88,738, Nov. [2, 1970, Pat. No. 3,722,833.

Foreign Application Priority Data Nov, 15, 1969 Japan 44-92248 Nov. 15, 1969 Japan 44-92249 References Cited UNITED STATES PATENTS 8/1909 Rippin 259/DlG. l

[ Aug. 20, 1974 3,543,966 12/1970 Ryan et al 259/72 X Primary Examiner-Harvey C. Hornsby Assistant Examiner-Philip R. Coe

Attorney, Agent, or FirmOwen, Wickersham & Erickson [57] ABSTRACT Pre-packaged dental filling ingredients for use by dentists. The ingredients which are in part liquid and in part powder are encapsulated and sealed tightly in a flexible-membrane formed bag and therein separated one from the other, which separation is released by the compression of the bag to cause the ingredients to be successively brought into contact and mixed together. The mixture, confined within the bag, is spatulated to form a paste or semi-solid, ready for application to patients tooth. The spatulation may be carried out advantageously with apparatus adapted to compressively roll over the flexible bag supported on a surface or squeeze on the bag against the surface.

6 Claims, 17 Drawing Figures PAiENlEuAuszomu FlG 8A APPARATUS FOR PREPARING A DENTAL FILLING This is division, of application Ser. No. 88,738, filed Nov. 12, 1970 now US. Pat. No. 3,722,833.

BACKGROUND OF THE INVENTION The invention is in the field of dentistry and especially relates to a new concept of dental filling and method of and apparatus for preparing a dental filling in paste or semi-solid form based on the new concept.

When a dentist prepares a dental filling from a plurality of ingredients a, it has hitherto been common requirement that he accurately measure out such ingredients from vials or the like containing individual ingredients and mix them together with instruments or utensils. This has been necessary because of the fact that they must be mixed together immediately before use. One of such ingredients is commonly a liquid or a number of different liquids and the other is a powder or a number of powders of different materials which are reactable or complementary to such liquid appropriate to the kind and type of a desired filling, and a suitable procedure must be made during the mixing stage to accomplish reactions uniformly over the entire region of the powder and liquid in a relatively short time. For example, when such a filling as zinc-phosphate, silicate or silico-phosphate cement is to be prepared, the liquid is an aqueous solution containing phosphoric acid, and the powder is made up from one or moreof zinc oxide, silicon oxide and aluminum oxide, along with one or more additives, the exact composition depending on the particular cement desired, and the powder and liq.- uid are mixed togetherand spatulated fully until the mixture becomes a paste which can be applied to a patients tooth or teeth. In phenomenon, when the powder and liquid are brought into contact, exothermic reactions are brought about to form phosphate, acid phosphate and other products in crystal and noncrystal forms, with the local crystalization being apparently followed by the solation and gelatin of the mixture while the paste commences and proceeds setting or curing with a final structure in which unreacted cores of powder are distributed among the reaction formed crystals.

Quantities of starting materials to be measured out and control of these complex reactions which are to be accomplished in a relatively short time are critical inasmuch as these are factors largely governing the final structure of the fully set product which determines the quality thereof as a dental filling. However, heretofore, these factors have been left to dentists who will attend to mixing or spatulation procedure in various conditions and at various levels of skill for such procedure. Moreover, it has been common, especially where spatulation procedure and the like is essential, that such is carried out with the mixture exposed to the environmental atmosphere whose conditions vary from season to season and from place to place. As a consequence, the strength and other quality characteristics of the resulting filling have largely varied depending on the humidity and the temperature of the particular environment in which it is prepared. The quality values have been often inferior to required standard values and this tendency is rather common in the humid and hot seasons.

SUMMARY OF THE INVENTION It is the primary object of the present invention, therefore, to provide an apparatus which makes it possible to prepare from a plurality of starting materials a dental filling of a superior quality, i.e., compressive strength, hardness, freedom of dimensional change (expansion or shrinkage), adhesiveness and interlockability, practically independently from the environmental conditions in which the filling is prepared.

Another object of the present invention is to provide apparatus for preparing a dental filling which relieves the dentists of the tedious bother of actually measuring out starting materials or ingredients as heretofore required and enables fabrication of a dental filling of superior characteristics to those heretofore obtained in standard conditions.

These objects and others which will become apparent hereinafter, are attained in accordance with the present invention, by our novel concept of packaging in mutual separation until just before use a plurality of premeasured substances adapted to form a dental filling, i.e., paste cement or amalgam, and releasing the separation to cause said separated substances to be successively brought into contact and mixed together and effecting reaction therebetween controlledly and uniformly within a confined space isolated from the atmosphere under compressive or squeeze action applied to the mixture. In accordance with an important aspect of the invention, there is provided a capsule comprising a flexible-membrane formed bag enclosing premeasured amounts of the substances which are tightly separated from one another in the bag, said separation being releasable by the compression of the bag to cause the substances to be successively mixed together within the bag, the latter being of thickness and material adapted to withstand said compression and for rupture or breakage only by the users purpose to take out the mixture or product for clinical use.

The invention is applicable to any of the dental fillings available and the plural substances for packaging in a bag are those choosen respectively depending on the particular end product desired. For example, for a zinc-phosphate cement, the first substance is a power containing zinc oxide and for a silicate cement, the powder contains mainly admixed silica and alumina. As is well known, various additives may be admixed to these oxides to facilitate and/or control exothermic reactions brought about as the primary constituent and a liquid are mixed together. Common to these particular cements, liquid is constituted by or contains an aqueous phosphoric acid solution. Also for a water settable phosphate cement, the powder may be of phosphate salt and/or acid phosphate salt and the liquid a suitable solvent such as water or alcohol. For amalgam, the liquid is mercury and the powder copper or copper alloy.

The bag may be a thin rubber, plastic, natural or synthetic resin and requisites of the material forming same are flexibility and toughness to withstand the compressive force applied thereto as well as non-destructability by liquid and exothermic reactions. Among others, a polyester has been found highly suitable for this purpose.

For the purpose of the present invention, the package is divided into plural compartments which are filled with a liquid or liquids and powder or powders, respectively, the package being tightly sealed to separate the contents from the environment. To this end, a pack may be prepared of a diaphragm filled with a liquid for enclosure as a first compartment within the flexible bag with the space between the outer surface of this diaphragm and the inner surface of the bag filled with powder forming the second compartment. In this case, the pack may comprise a plurality of or series of subpacks filled with liquid and distributed or embedded among the powder. To enable release of the separation between the liquid and the powder, the diaphragm forming the liquid pack may be of material, thickness or character to permit rupture by the compression of the outer flexible bag. Alternatively, the sealed package with plural separated compartments can be prepared by bonding portions of the bag so as to sealingly separate the liquid'or liquids from the powder or powders, this bond being sufficiently tight to prevent release of the separation in the absence of such compressive force as are applied to the bag for mixing purpose.

According to a preferred embodiment of the invention, a plurality of packages set forth above may be prepared which are disconnectably linked in series to permit the dentist to separate one from the series at his need.

The method of preparing a dental filling in a paste or semi-solid form making use of a sealed package with separated ingredients or starting substances, according to the present invention, includes applying a compressive, squeezing force to the flexible package supported on a suitable surface in the atmosphere or preferably within a coolant or temperature-controlled fluid so as to cause the separated substances to be successively brought into contact and spatulated sustaining reactions between them within the confined space of the package. While any known instrument may be used to spatulate the mixture left in the closed space, we prefer to this end the use of a rotary member adapted to unidirectionally reciprocatingly roll over the package against a supporting surface under compression or relatively concaved members or surfaces adapted to squeeze the package between them.

DESCRIPTION OF THE DRAWINGS FIG. 1A is a sectional view of a capsule embodying the principles of the present invention;

FIG. 1B is a cross-sectional view of the embodiment on the line lB-lB of FIG. 1A;

FIG. 2 is a sectional view of another form of the capsule according to the invention;

FIG. 3 is a plan view of another embodiment of the capsule according to the invention;

FIG. 4A is a plan view of a capsule of the invention embodied in another form;

FIG. 4B is a cross sectional view of the capsule taken on the line 4B4B of FIG. 4A;

FIG. 4C is a cross sectional view of a similar capsule;

FIG. 5 is a diagrammatic view of apparatus for performing the spatulation procedure according to the present invention;

FIG. 6 is a diagrammatic enlarged view illustrating a spatulating procedure according to the invention;

FIG. 7 is a diagrammatic top view of another form of a hand-operated spatulator according to the invention;

FIG. 7A is a side elevational view of the apparatus of FIG. 7.

FIG. 8 is a sectional view in a diagrammatic form of a motor-operated spatulator according to the present invention;

FIG. 8A is a top view in cross section of the spatulator of FIG. 8;

FIG. 9 is a diagrammatic representation of another form of spatulating apparatus according to the invention;

FIG. 10 is a side-elevational view of still another form of a motor-operated spatulator and FIG. 10A is a front view, partly fragmentary, thereof; and

FIG. 11 shows rotary members of various configurations useful in performing the spatulation procedure according to the present invention.

DETAILED DESCRIPTION In FIGS. 1A and 13 there is shown one illustrative embodiment of our novel dental capsule packaging a liquid and a powder in tight mutual separation. The capsule l is in the form of a closed bag made from a flexible membrane 2 whose interior is divided into multiple compartments filled with individual ingredients or starting substances, here, into two compartments 3 and 4 filled with a liquid and a powder, respectively, and separated by a flexible diaphragm 5. In this example, the latter diaphragm is of a material, thickness and character adapted to tightly separate liquid and powder normally but for rupture to release the separation when compressive, squeezing action is applied to the bag 1 as will be described. The membrane 2 forming the bag 1 is sufficiently flexible, tough and thick to withstand such compressive, squeezing action so as to confine the mixturewithin the space isolated from the environ ment. This capsule may be a pair of tubes closed at both ends with the first tube 5 filled with a premeasured amount of liquid and the second tube 2 containing a premeasured amount of powder in the space between its inner wall and the outer wall of the liquid-filled closed tube to form a sausage-shaped container with two compartments filled with liquid and powder respectively. For the users convenience, a plurality of such capsules may be prepared which are linked in series. Thus, the user can cut the portion c to separate the terminal capsule from the series for his intended use and spatulation procedure. The capsule of FIG. 2 is shown to include a liquid compartment 3 subdivided into plural compartments each filled with a amount of liquid complementary to those filled with the other subcompartments relative to an amount of powder contained in the bag 2 in contact therewith and the subcompartments. Each of the latter is adapted for rupture as compressive, squeezing action is exerted, as will be described.

In each single capsule which may be one of various forms as shown before and hereafter, it is of course necessary to package specific kinds of powder and liquid in accurately measured amounts and proportion depending on the type and amount of a particular dental filling. As set forth earlier, phosphate cements make use of a powder containing oxides and a liquid containing an phosphoric. acid solution, or otherwise a powder containing phosphate salt and a solvent liquid. The powder may include one or more additives to improve the quality of a final product as formed. While innumerable additives have been suggested by others, one

of the joint inventors of the present invention, Kiyoshi Inoue, has discovered that inclusion up to 5 percent by volume of finely divided fibers (of 0.1 to 3 micron diameter and 0.5 to 20 mm length) of a synthetic resin not detrimental to the tooth body (such as polypropylene, trifiuoride resin, vinyl chloride, chlorinated polyester, polyethylene, furan, epoxy resin, polyester, phenol resin and the like) greatly improves the compressive strength and the interlocking strength of any of these cements as applied to a tooth.

Shown in FIG. 3 is another embodiment of our novel capsule which is in the form of a rectangular, relatively flat envelope in which two compartments 3 and 4 sealed tightly from the environment are here again filled with a premeasured quantity of liquid and a premeasured quantity of powder respectively and interdivided by a boundary 5 for isolating the accurately measured liquid and powder from one another until just before a dental filling as the product therefrom is desired for use. This boundary is for the'indicated function as well as the function to release the isolation to cause these sealed contents to be mixed together. To this end, the capsule may be prepared by overlapping two flexible, plastic (e.g. polypropylene) sheets for a thickness, say, 0.05 mm and bonding the overlapped sheets permanently except those portions for forming compartments 3 and 4 and boundary 5', the latter being formed by tightly but fluid-pressure releasably bonding the corresponding overlapped portions of the sheets. In this case, the specific manner of bonding the sheets and filling liquid and powder may be that both elongated sides A and A of the overlapped sheets are permanently bonded and the sheets then semi-bonded along 5' or vice versa. Thence premeasured amounts of powder and liquid (e.g. 1.0 g powder and 0.36 cc liquid, for example, in the case of zinc phosphate cement) are entered into regions 4 and 3 (each with three sides closed) from open ends B and B, respectively and finally the regions B and B are permanently bonded to a two-compartment envelope as shown. The semi-bond at 5 is made at an adequeate tightness so as not to lose the bond under normal conditions but to do so when a squeezing action is applied to the envelope from region 3 to region 4 at a reasonable compressive force. To make such semi-bond and permanent-bond selectively, a conventional heat sealer is found highly suitable. In the mass production of a number of identical packages as shown, identical bonding or sealing conditions may be followed. To the completed envelope or package, designation of a filling to be made, liquid and powder contents and a specific manner of spatulation procedure may also be printed for the users convenience.

In FIGS. 4A and 48, there is shown another form of capsule which is here again a rectangular envelope formed from two plastic sheets permanently bonded along the margin and having releasably separated two compartments 3 and 4 filled with a liquid and a powder, respectively. The liquid-filled compartment 3 may be a tube of a rupturable diaphragm within the outer bag or envelope (FIG. 4B) and in contact with the powder filled compartment 4 as in FIG. 1A, or otherwise may be of membrane integral with the envelope and semibonded along boundaries 5" as in FIG. 4C to separate the liquid from the powder.

Thus, packages for the various types and amounts of various dental fillings can be prepared and distributed to dentists who may merely choose one package adapted for a particular clinical purpose without the need of actually attending to, as heretofore, the work of measuring out starting materials with high accuracy because of high criticality of such accuracy largely influencing the quality of the end product. The package, therefore, eliminates completely not only the dentists conventional need for such tedious preparatory work but also the deterioration of product fillings due to rough measuring of starting materials or entry of impurity as have been often the case heretofore.

In FIG. 5 there is shown in a diagrammatic view a spatulator 10 for forming a dental filling when used with a package illustrated in the foregoing figures. The spatulator includes a base 11 provided with a planar surface for supporting a package 1 securely in contact thereon with a pair of clamps 12a and 1212. It also is provided with a lever 13 whose one end 14 is hinged at a stand 15 secured to base 11 and its free end 16 is adapted for the users grip for the spatulation operation. Lever 13 has a cross arm 17 hinged at 18 which serves as a shank supporting a rotary member 19 adapted for free rotation about its axis 20 and the shank is also spring-held with the lever 13 as indicated. The rotary member 19 is thus adapted to reciprocatingly roll over the package 1 squeezing the latter against the supporting surface 11 as lever 16 is reciprocatingly swung. The initial compression of the package will rupture diaphragm 5 (FIGS. 1A, 1B, 2, and 4B) or release semi-bond 5, 5" (FIGS. 3 and 4C) to bring the liquid and powder together within the capsule, with the subsequent squeezing with the roller 19 causing the liquid and powder to be homogeneously mixed together effecting reaction as the compressed zone continuously shifts between the two relatively concave surfaces 19 and 11 as shown in FIG. 6. Therefore, unlike the conventional practice, not only is the spatulation advantageously carried out isolated from the humidity of the surrounding atmosphere, but also the heat generated by exothermic reactions is effectively scattered or dissipated by relatively large surfaces which rollingly squeeze the encapsulated mixture between them, with the quality of the resulting product filling bearing practically no dependency on the environmental conditions. Moreover, the spatulation with such an encapsulated mixture permits no entry of any impurity which would be detrimental to the quality of the product filling and does not soil the area used therefor.

having been attainable with standard techniques.

With usual dental fillings as prepared through chemical and curing reactions, the environmental temperature is sometimes or otherwise often critical to the quality of the filling prepared and applied for a given use where the temperature greatly influences the rates of reactions involved in the paste forming stage. While with the present invention, the heat generated by the exothermic reactions is effectively scattered and thus such reactions are advantageously held to proceed at moderate rates while the individual starting materials are brought into contact and spatulated together, it is sometimes desirable to control the environmental temperature especially where the latter differs much from an optimum or standard temperature at which particular filling materials are made into pastes. For such situations, a temperature control may be made here by maintaining the temperature of plate 11 at a desired value (e.g. circulating a temperature-control fluid therethrough or contacting a temperature control electronic element thereto) or preferably immersing in a temperature-control fluid the region of capsule 1 subjected to compressive squeezing action.

In FIG. 7, there is shown another form of handoperated spatulator according to the present invention. This embodiment includes a rotary member 119 which is rotatably supported by a grip 116 via a shaft 125 which is journaled either on roller 119 or grip 116 and secured with the other. On a spatulating plate 111, there is secured a package 1 such as is shown in FIG. 3 with a pair of spring clamps 1 12a and112b strecthing the package between them and the user may hold the package in a position and in contact with a supporting surface 111 with two fingers of his left hand. The operator may hold grip 116 with his right hand, bring rotary member 119 upon the package 1 and squeeze the package against surface 111. The peripheral surface of the rotary member is here made sufficiently frictional relative to the surface of package 1 and forming this member of a rubber and providing cracks thereon as shown are found highly advantageous to promote the squeezing action.

The spatulation process according to the present invention may also be carried out, when the economy permits, while passing an electric current of microampere order through the mixture subjected to compressive and squeezing action, using the principles set forth in copending Kiyoshi lnoue U.S. patent-application No. 873,204 to the advantages fully described therein. To this end, as shown in FIG. 7A an electromagnet 127 is provided behind spatulation plate 111 as wound by a coil 128 connectable with an alternating-current or pulse sources 129 via switch 130. It will be seen that the closure of switch 130 causes electromagnet 127 to create an oscillatory magnetic field which by electromagnetic induction creates an eddy current through the mixture spatulated within capsule 1. This electric treatment is found to yield to percent increase in hardness of resulting cements.

In FIGS. 8 and 8A, we show a motor-operated spatulator using a pair of rotary members 1 and 2 for compressively squeezing a capsule between them as they are relatively displaced. In this spatulator, the capsule is clamped on the periphery of first rotary member 1 along lb-lc as shown FIG. 8A, adapted in contact with the periphery of second rotary member 2 whose shaft 2a is rotatably secured to an arm 3 which at its one end 3a is hingedly secured to a cover table 9. The other end 31) of this arm is biased by a tension spring 4a connected with a biasing means so as to urge rotary surface 2 against first rotary member 1 at a suitable pressure adjusted by biasing means 4.

The drive means for these rotary members comprises a motor 5 mounted on base 8 and whose output shaft is connected by a reduction transmission 6 with the shaft la journaled through bearing 9b, to rotate the first rotary member 1 in one direction and to inductively rotate second rotary member 2 in the opposite direction by the friction between the contacting surfaces. Such rotary motion is preferably reciprocal rotary motion and, to this end, a rotation reciprocator 7 is provided for motor 5 and can be such that a predetermined angle of rotation in one direction of motor 5 operates a limit switch to reverse the direction of rotation of the motor.

In order to enable the operation in a temperature controlled condition which, as set forth earlier, is desirable when the environmental temperature differs considerably from an optimum or standard temperature at which the spatulation is to be made, the apparatus may be equipped with a suitable temperature control means. To this end, a housing 10 is here mounted on cover table 9 for reception of a coolant or temperature control liquid as supplied through a conduit 11 and a valve 12 and a suitable gasket 9a is provided to prevent leakage of the liquid which immerses rotary members 1 and 2 and the region of spatulation.

In operation, after a capsule is clamped on the specified location of the periphery of first rotary member 1, bias means 4 is adjusted to urge second rotary member 2 against the first at a pressure which would be sufficient to release the separation of the divided contents within the capsule when the latter is brought into the interface of these relatively urged members. Container 10 is mounted on cover 9 with gasket 9a and a fluid is fed into the container from pipe 1 1 by opening valve 12 until rollers l and 2 are sufficiently immersed within the liquid. Then, motor 5 is switched into drive and rotary member 1 carrying the package is reciprocatingly turned by an angle while rotary member 2 is inductively turned by the corresponding angle to reciprocatingly squeeze the capsule progressively compressed between them. The pressure increase of the liquid compartment during the initial turn will release the separation between the liquid and powder which are then homogeneously spatulated in situ within the confined space of the capsule by holding motor 5 in operation for a given time period. Therefore, the quality of the resulting product filling is totally independent of the users skill.

In the embodiment shown in FIG. 9, a capsule is again held on a rotary member 1 but a pair of other rotary members 2 and 2' each with a diameter greater than that of rotary member 1 are used to squeeze the capsule as the latter carried on first rotary member is urged against the other two rotary members alternately. Rotary member 2 is rotated in one direction by a motor 18 through a pulley 14a continuously and rotary member 2' is rotated in the opposite direction by a pulley connecting same with rotary member 2. A cam 13 is provided driven by a motor 18 synchronously with rotary members 2 and 2'. First rotary member 1 is rotatably held by a support member 1b which extends through a leaf spring 16 to an arm 15, these members being hingedat 15a and the one end of arm 15 being in contact with cam surface 13 as urged by expansion spring 17.

In FIGS. 10 and 10a, we show another form of I method and apparatus for performing the spatulation naled and resiliently held by spring 4 in an aperture 3a formed in an upright extending arm 3. The lower end 3c of this upright arm is pivotally secured to the lateral face of machine base 8 and hinged to make the arm 3 swingable in a plane perpendicular to spatulation surface 2a. Intermediary of the upper end portion 3a and the lower end 30, the arm is formed with an elongated aperture 3b of a length substantially equal to the diameter of a disk 5 as will be described. The disk 5 is rotated via a reduction transmission 7 by a motor 6 mounted on the base 8 and has on one of its face a protrusion 50 as shown which is adapted to be slidably engaged in aperture 3b so that the rotation of motor 6 causes protrusion 5a to travel along a circle while being slidably held in aperture 3b of the arm 3 which thus reciprocatingly swings over an angle about hinge 30 to cause rotary member 1 to reciprocatingly roll over surface 2a by friction compressing the package thereagainst under a 'pressure effected by spring 4.

In FIG. 11, there are shown rotary members of various forms which may be used with the foregoing apparatus. Each of these rotary members may be made from a plastic and preferably from a material having a high thermal conductivity such as aluminum to dissipate the heat generated by reactions to the extent that such reactions are carried on at a controlled rate. Also, if desired, a cooling element may be embedded in the rotary member.

We claim:

1. A dental apparatus for preparing a dental filling in paste form from a plurality of starting materials including a liquid and a powder encapsulated within a flexible bag with one separated from the other by a partition, said apparatus comprising:

a first member having a surface for securedly supporting said bag thereon,

a second member having a surface shiftable relative to said first surface and adapted to engage with said bag,

biasing means for urging said first and second members into mutual contact to form a common shiftable interface between said surfaces, and

motor means for relatively displacing said first and second members so as to reciprocatingly pass through said interface said bag under compression by the action of said biasing means to cause said partition to break and then said liquid and powder to be mixed together and spatulated to form a dental paste within said bag,

said second member comprising a first rotary member with at least a portion of the periphery surface thereof adapted to roll over said bag relative to said first member, said motor means being adapted to drive one of said first member and said first rotary member to provide the relative rolling motion therebetween,

said first member supporting said bag including a second rotary member having a shaft extending in a parallel relationship with that of said first rotary member, one of said first and second rotary members being driven by said motor and the other driven inductively by the friction between the contacting surfaces.

2. An apparatus as claimed in claim 1 wherein said motor means includes an electric motor and a rotation reciprocator coupled therewith for providing a periodically reversed rotary output to drive therewith said rotary members to reciprocatingly roll said bag therebetween.

3. An apparatus as claimed in claim 2 wherein said rotation reciprocator includes a sensor for sensing a predetermined angle of rotation in one direction of the motor and a limit switch responsive to said sensor for reversing the direction of rotation of the motor.

4. An apparatus as claimed in claim 1 wherein said second member further includes a third rotary member having a shaft extending in a parallel relationship with that of said first rotary member and being coupled therewith to rotate in a direction opposite to that in which the first rotary member rotates and said biasing means includes a cam arrangement adapted to urge said bag supported on said second rotary member against said first and third rotary members alternately.

thermal conductivity. 

1. A dental apparatus for preparing a dental filling in paste form from a plurality of starting materials including a liquid and a powder encapsulated within a flexible bag with one separated from the other by a partition, said apparatus comprising: a first member having a surface for securedly supporting said bag thereon, a second member having a surface shiftable relative to said first surface and adapted to engage with said bag, biasing means for urging said first and second members into mutual contact to form a common shiftable interface between said surfaces, and motor means for relatively displacing said first and second members so as to reciprocatingly pass through said interface said bag under compression by the action of said biasing means to cause said partition to break and then said liquid and powder to be mixed together and spatulated to form a dental paste within said bag, said second member comprising a first rotary member with at least a portion of the periphery surface thereof adapted to roll over said bag relative to said first member, said motor means being adapted to drive one of said first member and said first rotary member to provide the relative rolling motion therebetween, said first member supporting said bag including a second rotary member having a shaft extending in a parallel relationship with that of said first rotary member, one of said first and second rotary members being driven by said motor and the other driven inductively by the friction between the contacting surfaces.
 2. An apparatus as claimed in claim 1 wherein said motor means includes an electric motor and a rotation reciprocator coupled therewith for providing a periodically reversed rotary output to drive therewith said rotary members to reciprocatingly roll said bag therebetween.
 3. An apparatus as claimed in claim 2 wherein said rotation reciprocator includes a sensor for sensing a predetermined angle of rotation in one direction of the motor and a limit switch responsive to said sensor for reversing the direction of rotation of the motor.
 4. An apparatus as claimed in claim 1 wherein said second member further includes a third rotary member having a shaft extending in a parallel relationship with that of said first rotary member and being coupled therewith to rotate in a direction opposite to that in which the first rotary member rotates and said biasing means includes a cam arrangement adapted to urge said bag supported on said second rotary member against said first and third rotary members alternately.
 5. An apparatus as claimed in claim 1 wherein said first and second members are, at least at the region of said bag, disposed in a housing receiving fluid of a controlled temperature independent of the environmental temperature.
 6. An apparatus as claimed in claim 1 wherein said rotary member is formed of a material having a high thermal conductivity. 